1. Wyeth Research, 401 North Middletown Road, Pearl River, New York 10965, U.S.A., Wyeth Research, CN 8000, Princeton, New Jersey 08543, U.S.A., Wyeth Research, 1025 Boulevard Marcel-Laurin, Saint-Laurent, Quebec H4R 1J6, Canada, and Department of Chemistry, Princeton University, Princeton, New Jersey 08544, U.S.A.